Various food products can trigger disagreeable symptoms in certain people which are generally described as food intolerances. Given the complexity of the subject and the fact that a great deal remains to be learned about the mechanisms responsible for these reactions, the paper attempts to clarify the whole question. Food intolerances have been classified in various ways by different authors. The present paper considers only the three major groups: those due to enzyme deficiencies, those due to an allergic mechanism and those caused by histamine-release or histamine-releasing food products.